Pharmaceutical composition for treatment and prevention of cancer

ABSTRACT

An antibody or a fragment thereof having immunoreactivity to a polypeptide comprising not less than 7 continuous amino acids in the CD179b protein, which was identified as a cancer antigen protein specifically expressed on the surfaces of cancer cells, can be used as a pharmaceutical composition for therapy and/or prophylaxis of cancer.

This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Patent Application No. PCT/JP2009/062573 filed Jul. 10, 2009, which claims priority to Japanese Application Serial No. 2008-180057 filed on Jul. 10, 2008, and to Japanese Application Serial No. 2009-087379 filed on Mar. 31, 2009, the contents of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a novel pharmaceutical use of an antibody against CD179b or a fragment thereof, as an agent for therapy and/or prophylaxis of cancer.

BACKGROUND ART

Cancers are the commonest cause for death among all of the causes for death, and the therapies currently carried out therefor are mainly surgical treatment in combination with radiotherapy and chemotherapy. In spite of the developments of new surgical methods and discovery of new anti-cancer agents in recent years, treatment results of cancers are not improved very much at present except for some cancers. In recent years, by virtue of development in molecular biology and cancer immunology, cancer antigens recognized by antibodies and cytotoxic T cells which are specifically reactive with cancers, as well as the genes encoding the cancer antigens, were identified, and expectations for therapeutic methods specifically targeting cancer antigens have been raised (Non-patent Literature 1).

In a therapeutic method for cancer, to reduce side effects, it is desired that the peptide, polypeptide or protein recognized as the antigen exist hardly in normal cells and exist specifically in cancer cells. In 1991, Boon et al. in Ludwig Institute in Belgium isolated a human melanoma antigen MAGE 1 recognized by CD8-positive T cells by a cDNA-expression cloning method using an autologous cancer cell line and cancer-reactive T cells (Non-patent Literature 2). Thereafter, the SEREX (serological identifications of antigens by recombinant expression cloning) method, wherein tumor antigens recognized by antibodies produced in the living body of a cancer patient in response to the cancer of the patient himself are identified by application of a gene expression cloning method, was reported (Non-patent Literature 3; Patent Literature 1), and several cancer antigens which are hardly expressed in normal cells while being specifically expressed in cancer cells have been isolated by this method (Non-patent Literatures 4 to 9). Further, using a part thereof as targets, clinical tests for cell therapies using immunocytes specifically reactive with the cancer antigens, and cancer-specific immunotherapies such as those using vaccines containing the cancer antigens have been carried out.

On the other hand, in recent years, various antibody drugs for therapy of cancer have become conspicuous in the world, which drugs target antigen proteins on cancer cells. Since certain levels of pharmacological effects can be obtained with such antibody drugs as cancer-specific therapeutic agents, they are drawing attention, but most of the antigen proteins to be targeted are those also expressed in normal cells, so that, as a result of administration of the antibody, not only cancer cells, but also normal cells expressing the antigen are damaged, resulting in occurrence of side effects, which has been problematic. Thus, it is expected that identification of cancer antigens specifically expressed on the surfaces of cancer cells and employment of antibodies targeting these as drugs will allow therapy with antibody drugs with less side effects.

CD179b is known to be a part of the surrogate light chain of immunoglobulin and expressed on the membrane surfaces of precursor cells of B cells (pre-B cells and pro-B cells). It disappears upon differentiation of B cells and is not expressed in mature B cells. However, CD179b is known to be expressed in leukemia (pre-B cell leukemia) cells produced by cancerization of pre-B cells (Non-patent Literatures 10 and 11). Further, CD179b is known to be expressed also in lymphoma (pre-B cell lymphoma) cells produced by cancerization of pre-B cells, and able to be used as a diagnostic marker for pre-B cell lymphoma (Non-patent Literature 12). However, its specific expression has not been reported for leukemia cells other than pre-B cell leukemia cells, lymphomas other than pre-B cell lymphoma, breast cancer cells and the like. Further, there has been no report suggesting that antibodies against CD179b are useful for therapy and/or prophylaxis of cancer.

PRIOR ART LITERATURES Patent Literature

-   Patent Literature 1: U.S. Pat. No. 5,698,396 B

Non-Patent Literatures

-   Non-patent Literature 1: Tsuyoshi Akiyoshi, “Cancer and     Chemotherapy”, 1997, Vol. 24, pp. 551-519 -   Non-patent Literature 2: Bruggen P. et al., Science, 254:1643-1647     (1991) -   Non-patent Literature 3: Proc. Natl. Acad. Sci. USA, 92:11810-11813     (1995) -   Non-patent Literature 4: Int. J. Cancer, 72:965-971 (1997) -   Non-patent Literature 5: Cancer Res., 58:1034-1041 (1998) -   Non-patent Literature 6: Int. J. Cancer, 29:652-658 (1998) -   Non-patent Literature 7: Int. J. Oncol., 14:703-708 (1999) -   Non-patent Literature 8: Cancer Res., 56:4766-4772 (1996) -   Non-patent Literature 9: Hum. Mol. Genet 6:33-39 (1997) -   Non-patent Literature 10: Adv. Immunol., 63:1-41 (1996) -   Non-patent Literature 11: Blood, 92:4317-4324 (1998) -   Non-patent Literature 12: Modern Pathology, 17:423-429 (2004)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention aims to identify cancer antigen proteins specifically expressed on the surfaces of cancer cells and provide uses of antibodies targeting them as agents for therapy and/or prophylaxis of cancer.

Means for Solving the Problems

The present inventors intensively studied to obtain, by the SEREX method using serum from a patient dog from which a canine breast cancer tissue-derived cDNA library was prepared, cDNA encoding a protein which binds to antibodies existing in the serum derived from the cancer-bearing living body, and, based on a human gene homologous to the obtained gene, human CD179b having the amino acid sequence shown in SEQ ID NO:3 was prepared. Further, the present inventors discovered that CD179b is hardly expressed in normal tissues, but specifically expressed in breast cancer, leukemia and lymphoma cells. Further, the present inventors discovered that antibodies against such CD179b damage cancer cells expressing CD179b, thereby completing the present invention.

Thus, the present invention has the following characteristics.

The present invention provides a pharmaceutical composition for therapy and/or prophylaxis of cancer comprising as an effective component an antibody or a fragment thereof, the antibody having immunoreactivity to a CD179b protein having the amino acid sequence shown in SEQ ID NO:3 or an amino acid sequence having a sequence identity of not less than 60% with the amino acid sequence, or to a fragment thereof comprising not less than 7 continuous amino acids.

In its mode, the above cancer is a cancer expressing the CD179b gene.

In another mode, the above cancer is breast cancer, leukemia or lymphoma.

In another mode, the antibody is a monoclonal antibody or a polyclonal antibody.

In another mode, the antibody is a human antibody, humanized antibody, chimeric antibody, single-chain antibody or bispecific antibody.

In another mode, the above antibody is an antibody comprising a heavy chain variable region having the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 and a light chain variable region having the amino acid sequences shown in SEQ ID NOs:106, 107 and 108, the antibody having immunoreactivity to a CD179b protein.

In another mode, the above antibody is an antibody comprising a heavy chain variable region having the amino acid sequence shown in SEQ ID NO:105 and a light chain variable region having the amino acid sequence shown in SEQ ID NO:109, the antibody having immunoreactivity to a CD179b protein.

The present invention further provides the following antibodies.

(i) An antibody comprising a heavy chain variable region having the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 and a light chain variable region having the amino acid sequences shown in SEQ ID NOs:106, 107 and 108, the antibody having immunoreactivity to a CD179b protein.

(ii) An antibody comprising a heavy chain variable region having the amino acid sequence shown in SEQ ID NO:105 and a light chain variable region having the amino acid sequence shown in SEQ ID NO:109, the antibody having immunoreactivity to a CD179b protein.

(iii) The antibodies of the above (i) and (ii), having cytotoxic activity.

(iv) The antibodies of the above (i) and (ii), each of which is a humanized antibody, chimeric antibody, single-chain antibody or bispecific antibody.

The present invention further provides the following polypeptides or DNAs.

(v) A DNA encoding a polypeptide having the amino acid sequence shown in SEQ ID NO:105, or a DNA encoding the polypeptide.

(vi) A DNA encoding a polypeptide having the amino acid sequence shown in SEQ ID NO:109, or a DNA encoding the polypeptide.

(vii) A DNA having the base sequence shown in SEQ ID NO:110.

(viii) A DNA having the base sequence shown in SEQ ID NO:111.

(ix) A heavy-chain complementarity-determining region (CDR) polypeptide selected from the group consisting of the amino acid sequences shown in SEQ ID NOs:103, 104 and 102, or a DNA encoding the polypeptide.

(x) A light-chain complementarity-determining region (CDR) polypeptide selected from the group consisting of the amino acid sequences shown in SEQ ID NOs:106, 107 and 108, or a DNA encoding the polypeptide.

Effect of the Invention

The antibody against CD179b, which is used in the present invention damages cancer cells. Therefore, the antibody against CD179b is useful for therapy and/or prophylaxis of cancer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the expression patterns of the gene encoding the CD179b protein in normal tissues and tumor cell lines. Reference numeral 1 represents the expression pattern of the gene encoding the CD179b protein; and reference numeral 2 represents the expression pattern of the GAPDH gene.

FIG. 2 is a diagram showing an anti-tumor effect of an antibody against CD179b (anti-CD179b monoclonal antibody #8) in nude mice to which a human cancer cell line Namalwa expressing CD179b was transplanted. Reference numeral 3 represents the size of the tumor in miceto which the anti-CD179b monoclonal antibody #8 was administered; and reference numeral 4 represents the size of the tumor in mice to which PBS(−) was administered.

BEST MODE FOR CARRYING OUT THE INVENTION

The amino acid sequence shown in SEQ ID NO:3 in SEQUENCE LISTING disclosed in the present invention is the amino acid sequence of CD179b isolated, by the SEREX method using serum from a patient dog from which a canine mammary gland cancer tissue-derived cDNA library was prepared, as a human homologous factor (homologue) of a polypeptide which binds to antibodies specifically existing in the serum derived from the cancer-bearing dog (see Example 1). The antibody against CD179b used in the present invention may be any type of antibody as long as the antibody can exert an anti-tumor activity, and examples thereof include monoclonal antibodies, polyclonal antibodies, synthetic antibodies, multispecific antibodies, human antibodies, humanized antibodies, chimeric antibodies, single chain antibodies (scFv), and antibody fragments such as Fab and F(ab′)₂. These antibodies and fragments thereof can be prepared by methods known to those skilled in the art. In the present invention, the antibody can preferably specifically bind to a CD179b protein, and, in cases where the subject is a human, the antibody is preferably a human antibody or a humanized antibody in order to avoid or suppress rejection reaction.

Here, the term “specifically bind to a CD179b protein” means that the antibody specifically binds to a CD179b protein and does not substantially bind to other proteins.

In the present invention, the antibody against CD179b employed may be commercially available. Examples of known antibodies against human CD179b include clones such as GA170, H-60, HP6054, A-19, C-16, SLC1, SLC2, SLC3, SLC4 and HSL11, which are available.

The anti-tumor activity of the antibody which may be used in the present invention can be assayed in vitro by investigating whether or not the antibody shows cytotoxicity against tumor cells expressing the polypeptide via immunocytes or complement, as mentioned later.

Further, the subject of the present invention to be subjected to the therapy and/or prophylaxis of cancer is a mammal such as a human, pet animal, domestic animal or sport animal, and the subject is preferably human.

The terms “cancer” and “tumor” used in the present specification mean a malignant neoplasm, and are used interchangeably.

Preparation of antigens, preparation of antibodies, and pharmaceutical compositions, related to the present invention will now be described.

<Preparation of Antigens for Preparation of Antibodies>

The animal species from which the protein or a fragment thereof used as a sensitizing antigen to obtain an antibody against CD179b used in the present invention is derived is not restricted, and examples thereof include human, dog, bovine, mouse and rat. However, the animal species is preferably selected in consideration of the compatibility with the parent cells used for cell fusion, and, in general, a protein derived from a mammal, especially human, is preferred. For example, in cases where the CD179b is human CD179b, a human CD179b protein or a partial peptide thereof, cells expressing human CD179b, or the like may be used.

The base sequences and the amino acid sequences of human CD179b and homologues thereof can be obtained by, for example, accessing GenBank (NCBI, USA) and using an algorithm such as BLAST or FASTA (Karlin and Altschul, Proc. Natl. Acad. Sci. U.S.A., 90:5873-5877, 1993; Altschul et al., Nucleic Acids Res., 25:3389-3402, 1997). CD179b is also called as λ5, IGLL1, Vpreb2, LOC608248 or the like, but “CD179b” is used as a representative in the present specification. For example, human CD179b is registered under the numbers such as NM_152855 and NM_020070; murine Vpreb2 is registered under the numbers such as NM_016983; and canine LOC608248 is registered under the numbers such as XM_845215.

In the present invention, in cases where the base sequence or the amino acid sequence of human CD179b is used as a standard, a nucleic acid or a protein is targeted which has a sequence showing a sequence identity of 50% to 100%, preferably 60% to 100%, more preferably 80% to 100%, still more preferably 90% to 100%, most preferably 95% to 100%, for example, 97% to 100%, 98% to 100%, 99% to 10% or 99.5% to 100% to the sequence shown in SEQ ID NO:1 or 3. Here, the term “% sequence identity” means the percentage (%) of identical amino acids (or bases) with respect to the total number of amino acids (or bases) when two sequences are aligned with each other such that the maximum similarity is achieved therebetween with or without introduction of a gap(s).

The length of the fragment of the CD179b protein is not less than the length of amino acids of the epitope (antigenic determinant), which is the shortest unit recognized by the antibody, and less than the total length of the protein. The length of the epitope is normally within the range of 7 to 12 continuous amino acids.

The above-described human CD179b protein and polypeptides containing its partial peptides can be synthesized by a chemical synthesis method such as the Fmoc method (fluorenyl-methyloxycarbonyl method) or the tBoc method (t-butyloxycarbonyl method). Further, they can be synthesized by conventional methods using various types of commercially available peptide synthesizers. Further, the polypeptide of interest can be obtained using known genetic engineering techniques, by preparing a polynucleotide encoding the above polypeptide and incorporating the polynucleotide into an expression vector, which is then introduced into a host cell, followed by allowing the polypeptide to be produced in the host cell.

The polynucleotide encoding the above polypeptide can be easily prepared by a known genetic engineering technique or a conventional method using a commercially available nucleic acid synthesizer. For example, DNA having the base sequence shown in SEQ ID NO:1 can be prepared by carrying out PCR using human chromosomal DNA or a human cDNA library as a template, and a pair of primers designed such that the base sequence shown in SEQ ID NO:1 can be amplified therewith. The reaction conditions for the PCR can be set appropriately, and examples thereof include, but are not limited to, repeating the reaction process of 94° C. for 30 seconds (denaturation), 55° C. for 30 seconds to 1 minute (annealing) and 72° C. for 2 minutes (extension) for, for example, 30 cycles, followed by the reaction at 72° C. for 7 minutes. Further, the desired DNA can be isolated by preparing an appropriate probe(s) or primer(s) based on the information of the base sequence and the amino acid sequence shown in SEQ ID NOs:1 and 3, respectively, in SEQUENCE LISTING in the present specification, and using the probe(s) or primer(s) for screening of a cDNA library of human or the like.

The cDNA library is preferably prepared from cells, an organ or a tissue expressing the protein of SEQ ID NO:3. Examples of such cells and a tissue include bone marrow, leukemia cells, breast cancer cells and lymphoma cells. The above-described operations such as preparation of the probe(s) or primer(s), construction of a cDNA library, screening of the cDNA library and cloning of the gene of interest are known to those skilled in the art, and can be carried out according to the methods described in, for example, Sambrook et al., Molecular Cloning, Second Edition, Current Protocols in Molecular Biology (1989). From the thus obtained DNA, a DNA encoding a human CD179b protein or a partial peptide thereof can be obtained.

The above-described host cells may be any cells as long as they can express the above polypeptide, and examples of prokaryotic cells include, but are not limited to, E. coli, and examples of eukaryotic cells include, but are not limited to, mammalian cultured cells such as the monkey kidney cells COS 1, Chinese hamster ovary cells CHO, human fetal kidney cell line HEK 293 and mouse embryonic skin cell line NIH3T3; yeast cells such as budding yeasts and fission yeasts; silkworm cells; and Xenopus egg cells.

In cases where prokaryotic cells are used as the host cells, the expression vector employed in the prokaryotic cells has a replication origin, promoter, ribosome binding site, multicloning site, terminator, drug resistant gene, nutrient complementary gene and/or the like. Examples of the expression vector for E. coli include the pUC system, pBluescriptII, pET expression system and pGEX expression system. By incorporating a DNA encoding the above polypeptide into such an expression vector and transforming prokaryotic host cells with the vector, followed by culturing the resulting transformants, the polypeptide encoded by the DNA can be expressed in the prokaryotic host cells. In this process, the polypeptide can also be expressed as a fusion protein with another protein (e.g., green fluorescent protein (GFP) or glutathione S-transferase (GST)).

In cases where eukaryotic cells are used as the host cells, an expression vector for eukaryotic cells having a promoter, splicing site, poly(A) addition site and/or the like is used as the expression vector. Examples of such an expression vector include pKA1, pCDM8, pSVK3, pMSG, pSVL, pBK-CMV, pBK-RSV, EBV vector, pRS, pcDNA3, pMSG and pYES2. In the same manner as described above, by incorporating a DNA encoding the above polypeptide into such an expression vector and transforming eukaryotic host cells with the vector, followed by culturing the resulting transformants, the polypeptide encoded by the DNA can be expressed in the eukaryotic host cells. In cases where pINDN5-His, pFLAG-CMV-2, pEGFP-N1, pEGFP-C1 or the like is used as the expression vector, the above polypeptide can be expressed as a fusion protein to which a tag such as His tag (e.g., (His)₆ to (His)₁₀), FLAG tag, myc tag, HA tag or GFP was added.

For the introduction of the expression vector into the host cells, well-known methods such as electroporation, the calcium phosphate method, the liposome method, the DEAE dextran method and microinjection can be used.

Isolation and purification of the polypeptide of interest from the host cells can be carried out by a combination of known separation operations. Examples of the known separation operations include, but are not limited to, treatment with a denaturant such as urea, or a surfactant; ultrasonication treatment; enzyme digestion; salting-out or solvent fractional precipitation; dialysis; centrifugation; ultrafiltration; gel filtration; SDS-PAGE; isoelectric focusing; ion-exchange chromatography; hydrophobic chromatography; affinity chromatography; and reversed-phase chromatography.

<The Structure of an Antibody>

An antibody is usually a heteropolymeric glycoprotein having at least two heavy chains and two light chains. Except for IgM, it is a heterotetrameric glycoprotein of about 150 kDa constituted by two identical light (L) chains and two identical heavy (H) chains. Typically, each light chain is linked to a heavy chain via a single disulfide covalent bond, but the number of disulfide bonds between the heavy chains varies among various immunoglobulin isotypes. Each of the heavy chains and the light chains also has intrachain disulfide bonds. Each heavy chain has a variable domain (VH region) in its one end, and the variable domain is followed by several constant regions. Each light chain has a variable domain (VL region), and has one constant region at the opposite end thereof. The constant region of each light chain is aligned with the first constant region of a heavy chain, and each light chain variable domain is aligned with a heavy chain variable domain. Each variable domain of an antibody has particular regions showing particular variabilities, called the complementarity-determining regions (CDRs), which give a binding specificity to the antibody. Parts in each variable region, which parts are relatively conserved are called the framework regions (FRs). Each of the complete variable domains of the heavy chains and the light chains has four FRs linked via three CDRs. In each heavy chain, the three CDRs are called CDRH1, CDRH2 and CDRH3 in the order from the N-terminus, and, in each light chain, they are called CDRL1, CDRL2 and CDRL3 in a similar manner. For the binding specificity of an antibody against an antigen, CDRH3 is most important. Further, the CDRs in each strand are held together by the FR regions such that the CDRs are close to one another, thereby contributing to formation of an antigen-binding site together with the CDRs from another strand. Although the constant region does not directly contribute to binding of the antibody to an antigen, it shows various effector functions such as involvement in antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis via binding to the Fcγ receptor, the half life/clearance rate via the Neonatal Fc receptor (FcRn), and complement-dependent cytotoxicity (CDC) via the C1q component of the complement cascade.

<Preparation of the Antibody>

The anti-CD179b antibody in the present invention means an antibody having an immunological reactivity with the total length of the CD179b protein or a fragment thereof. Here, the term “immunological reactivity” means a property by which the antibody and a CD179b antigen are bound to each other, and the function to damage (to cause death, suppression or regression of) tumors is exerted by such binding. That is, the type of the antibody used in the present invention is not restricted as long as the antibody can be bound to a CD179b protein to damage tumors such as breast cancer, leukemia, and lymphoma.

Examples of the antibody include monoclonal antibodies, polyclonal antibodies, synthetic antibodies, multispecific antibodies, human antibodies, humanized antibodies, chimeric antibodies, single chain antibodies, and antibody fragments (e.g., Fab and (Aab′)₂). Further, the antibody belongs to an arbitrary class of an immunoglobulin molecule, such as IgG, IgE, IgM, IgA, IgD or IgY, or to an arbitrary subclass such as IgG1, IgG2, IgG3, IgG4, IgA1 or IgA2.

The antibody may be further modified by glycosylation, acetylation, formylation, amidation, phosphorylation, pegylation (PEG) and/or the like.

Preparation examples of various antibodies are described below.

In cases where the antibody is a monoclonal antibody, for example, a leukemia cell line Namalwa expressing CD179b is administered to a mouse to immunize the mouse, and spleen is extracted from the mouse. Cells are separated and fused with mouse myeloma cells, and, from the obtained fused cells (hybridomas), a clone producing an antibody having a cancer cell growth suppressing action is selected. By isolating the monoclonal antibody-producing hybridoma having a cancer cell growth suppressing action, and culturing the hybridoma, followed by purifying the antibody from the culture supernatant by a commonly-used affinity purification method, the antibody can be prepared.

A hybridoma which produces a monoclonal antibody can also be prepared, for example, as follows.

First, according to a known method, an animal is immunized with a sensitizing antigen. In general, the method is carried out by intraperitoneal or subcutaneous injection of the sensitizing antigen to a mammal More particularly, the sensitizing antigen is diluted to an appropriate volume with PBS (Phosphate-Buffered Saline) or physiological saline and suspended, followed by mixing, as desired, an appropriate amount of a normal adjuvant such as Freund's complete adjuvant with the suspension. This is followed by emulsification, and then administration of the emulsion to a mammal every 4 to 21 days for several times. Further, it is also possible to use an appropriate carrier when the immunization with the sensitizing antigen is carried out.

After such immunization of a mammal and confirmation of increase in the serum level of the desired antibody, immunocytes are collected from the mammal and subjected to cell fusion. Examples of preferred immunocytes especially include spleen cells.

As the other parent cells to be fused with the immunocytes, mammalian myeloma cells are used. Examples of the myeloma cells preferably employed include various known cell lines such as P3U1 (P3-X63Ag8U1), P3 (P3x63Ag8.653) (J. Immnol (1979) 123, 1548-1550), P3x63Ag8U.1 (Current Topics in Microbiology and Immunology (1978) 81, 1-7), NS-1 (Kohler. G. and Milstein, C. Eur. J. Immunol. (1976) 6, 511-519), MPC-11 (Margulies. D. H. et al., Cell (1976) 8, 405-415), SP2/0 (Shulman, M. et al., Nature (1978) 276, 269-270), FO (deSt. Groth, S. F. et al., J. Immunol. Methods (1980) 35, 1-21), S194 (Trowbridge, I. S. J. Exp. Med. (1978) 148, 313-323) and 8210 (Galfre, G. et al., Nature (1979) 277, 131-133).

The cell fusion between the immunocytes and the myeloma cells can be carried out basically according to a known method, for example, a method by Kohler and Milstein (Kohler. G. and Milstein, C., Methods Enzymol. (1981) 73, 3-46).

More particularly, the cell fusion is carried out, for example, in the presence of a cell fusion-promoting agent, in a normal nutrient medium. Examples of the fusion-promoting agent include polyethylene glycol (PEG) and Sendai virus (HVJ), and, in order to enhance the fusion efficiency, an auxiliary agent such as dimethylsulfoxide may also be added as desired.

The ratio between the immunocytes and the myeloma cells to be used may be arbitrarily set. For example, it is preferred to use 1 to 10 times more immunocytes than the myeloma cells. Examples of the medium which can be used for the cell fusion include the RPMI1640 medium which is preferred for the growth of the myeloma cell line; MEM medium; and other media normally used for this kind of cell culture. Further, a serum replacement such as fetal calf serum (FCS) can also be used in combination.

During the cell fusion, prescribed amounts of the immunocytes and the myeloma cells are mixed together well in the medium, and a PEG solution (with an average molecular weight of about 1000 to 6000, for example) preheated to about 37° C. is added to a concentration of normally 30 to 60% (w/v), followed by mixing the resulting mixture to form the hybridoma of interest. Subsequently, by repeating the operation of successive addition of an appropriate medium and removal of the supernatant by centrifugation, cell fusion agents and the like which are not preferred for the growth of the hybridoma are removed.

The thus obtained hybridoma is selected by being cultured in a normal selection medium such as the HAT medium (a medium containing hypoxanthine, aminopterin and thymidine). The culture in the above HAT medium is continued for a length of time sufficient for the cells other than the hybridoma of interest (unfused cells) to die (normally, for several days to several weeks). Thereafter, a normal limiting dilution method is carried out for screening and cloning of a single hybridoma producing the antibody of interest.

In addition to the method in which the above hybridoma is obtained by immunizing a non-human animal with the antibody, there is also a method in which human lymphocytes, such as human lymphocytes infected with EB virus, are sensitized in vitro with a protein, protein-expressing cells or a lysate thereof, and the sensitized lymphocytes are fused with human-derived myeloma cells having a permanent division potential, for example, U266 (registration number TIB196), to obtain a hybridoma producing a human antibody having a desired activity (cell growth suppression activity, for example).

The thus prepared hybridoma producing a monoclonal antibody can be subcultured in a normal medium, and can be stored in liquid nitrogen for a long period.

That is, the hybridoma can be prepared by a process wherein the desired antigen or cells expressing the desired antigen is/are used as a sensitizing antigen to carry out immunization according a conventional immunization method, thereby obtaining immunocytes, which are then fused with known parent cells by a conventional cell fusion method, followed by screening of monoclonal antibody-producing cells (hybridomas) by a conventional screening method.

Another example of the antibody which can be used in the present invention is a polyclonal antibody. The polyclonal antibody can be obtained, for example, as follows.

A naturally occurring CD179b protein, or a recombinant CD179b protein expressed as a fusion protein with GST in a microorganism such as E. coli, or a partial peptide thereof is used for immunization of a small animal such as a mouse, human antibody-producing mouse or rabbit, and serum is obtained from the small animal. A polyclonal antibody is prepared by purifying the serum by, for example, ammonium sulfate precipitation, protein A and protein G columns, DEAE ion-exchange chromatography, or an affinity column coupled with a CD179b protein or a synthetic peptide.

Here, known examples of the human antibody-producing mouse include the KM mouse (Kirin Pharma/Medarex) and XenoMouse (Amgen). When such a mouse is immunized with a CD179b protein or a fragment thereof, a complete human polyclonal antibody can be obtained from blood. Further, by removing spleen cells from the immunized mouse and subjecting the cells to the fusion method with myeloma cells, a human-type monoclonal antibody can be prepared.

The antigen can be prepared according to a method using animal cells (Japanese Translated PCT Patent Application Laid-open No. 2007-530068), a method using a baculovirus (e.g., WO98/46777), or the like. In cases where the immunogenicity of the antigen is low, the immunization may be carried out after binding the antigen to a macromolecule having immunogenicity, such as albumin.

Further, a gene recombinant antibody can also be used, which antibody was prepared by cloning the antibody gene from the hybridoma and incorporating it into an appropriate vector, which was then transfected to a host, followed by allowing the host to produce the antibody by the genetic recombination technique (for example, see Carl, A. K. Borrebaeck, James, W. Larrick, THERAPEUTIC MONOCLONAL ANTIBODIES, Published in the United Kingdom by MACMILLAN PUBLISHERS LTD, 1990).

More particularly, cDNA of the variable region (V region) of the antibody is synthesized from mRNA of the hybridoma using a reverse transcriptase. After obtaining the DNA encoding the V region of the antibody of interest, the DNA is linked to DNA encoding the antibody constant region (C region) of interest, and the resultant is incorporated into an expression vector. Alternatively, the DNA encoding the V region of the antibody may be incorporated into an expression vector having the DNA of the antibody C region. The incorporation is carried out such that the expression is allowed under the controls by expression control regions such as an enhancer and/or a promoter. Subsequently, host cells can be transformed with this expression vector to allow expression of the antibody.

The anti-CD179b antibody of the present invention is preferably a monoclonal antibody. However, it may also be a polyclonal antibody, genetically modified antibody (such as a chimeric antibody or humanized antibody) or the like.

Examples of the monoclonal antibody include human monoclonal antibodies and non-human animal monoclonal antibodies (e.g., mouse monoclonal antibodies, rat monoclonal antibodies and chicken monoclonal antibodies). The monoclonal antibody can be prepared by culturing a hybridoma obtained by fusion of spleen cells from a non-human mammal (e.g., mouse or human antibody-producing mouse) immunized with a CD179b protein, with myeloma cells. In Examples below, a mouse monoclonal antibody #8 was prepared, with which an anti-tumor effect was confirmed. The antibody #8 has a heavy chain variable (VH) region having the amino acid sequence shown in SEQ ID NO:105 and a light chain variable region (VL) having the amino acid sequence shown in SEQ ID NO:109. Here, the VH region has the amino acid sequences shown in SEQ ID NO:103 (CDR1), SEQ ID NO:104 (CDR2) and SEQ ID NO:102 (CDR3); and the VL region has the amino acid sequences shown in SEQ ID NO:106 (CDR1), SEQ ID NO:107 (CDR2) and SEQ ID NO:108 (CDR3).

A chimeric antibody is an antibody prepared by combining sequences derived from different animals. Examples thereof include an antibody having variable regions of the heavy chain and the light chain of a mouse antibody and the constant regions of the heavy chain and the light chain of a human antibody. Preparation of the chimeric antibody can be carried out using a known method. For example, it can be obtained by linking a DNA encoding an antibody V region to a DNA encoding a human antibody C region, followed by incorporating the resultant to an expression vector and transfecting the vector to a host, thereby allowing production of a chimeric antibody.

Examples of the polyclonal antibody include antibodies obtained by immunizing a human antibody-producing animal (mouse, for example) with a CD179b protein

A humanized antibody is a modified antibody also called as a reshaped human antibody. A humanized antibody can be constructed by transplantation of the CDRs of an antibody derived from an immunized animal to the complementarity-determining regions of a human antibody. A common genetic recombination technique therefor is known.

More particularly, a DNA sequence designed such that the CDRs of a mouse antibody are linked to the framework regions (FRs) of a human antibody is synthesized by the PCR method from several oligonucleotides prepared such that the oligonucleotides have overlapped regions in their ends. The obtained DNA is linked to a DNA encoding the human antibody constant region, and the resultant is incorporated into an expression vector, followed by introducing the vector to a host, to obtain a humanized antibody (see European Patent Application Publication No. EP 239400 and International Patent Application Publication No. WO96/02576). The FRs of the human antibody linked via the CDRs are selected such that the complementarity-determining regions form a good antigen-binding site. As required, amino acids in the framework regions in the variable regions of the antibody may be substituted such that the complementarity-determining regions of the reshaped human antibody form an appropriate antigen-binding site (Sato, K. et al., Cancer Res. (1993) 53, 851-856). Further, the framework regions may be substituted with framework regions derived from various human antibodies (see International Patent Application Publication No. WO99/51743).

After preparation of a chimeric antibody or a humanized antibody, amino acids in the variable regions (FRs, for example) and/or the constant regions may be substituted with other amino acids.

The number of the amino acids to be substituted is, for example, less than 15, less than 10, not more than 8, not more than 7, not more than 6, not more than 5, not more than 4, not more than 3 or not more than 2, preferably 1 to 5, more preferably 1 or 2, and the substituted antibody should be functionally equivalent to the unsubstituted antibody. The substitutions are preferably conservative amino acid substitutions, which are substitutions among amino acids having similar properties of charges, side chains, polarities, aromaticities and/or the like. The amino acids having similar properties can be classified, for example, into basic amino acids (arginine, lysine and histidine), acidic amino acids (aspartic acid and glutamic acid), uncharged polar amino acids (glycine, asparagine, glutamine, serine, threonine, cysteine and tyrosine), nonpolar amino acids (leucine, isoleucine, alanine, valine, proline, phenylalanine, tryptophan and methionine), branched chain amino acids (threonine, valine and isoleucine) and aromatic amino acids (phenylalanine, tyrosine, tryptophan and histidine).

Examples of the modified antibody include antibodies bound to various molecules such as polyethylene glycol (PEG). In the modified antibody of the present invention, the substance to which the antibody is bound is not restricted. Such a modified antibody can be obtained by chemical modification of the obtained antibody. These methods are already established in the art.

Here, the term “functionally equivalent” means, for example, that the subject antibody has a similar biological or biochemical activity, more particularly, a function to damage tumors, and does not essentially cause the rejection reaction when it is applied to human. Examples of such an activity may include a cell growth suppressing activity and a binding activity.

As a method well-known to those skilled in the art for preparation of a polypeptide functionally equivalent to a certain polypeptide, introduction of a mutation(s) to a polypeptide is known. For example, those skilled in the art can use site-directed mutagenesis (Hashimoto-Gotoh, T. et al. (1995) Gene 152, 271-275; Zoller, M J, and Smith, M. (1983) Methods Enzymol. 100, 468-500; Kramer, W. et al. (1984) Nucleic Acids Res. 12, 9441-9456; Kramer W, and Fritz H J (1987) Methods. Enzymol. 154, 350-367; Kunkel, T A (1985) Proc Natl Acad Sci USA. 82, 488-492; Kunkel (1988) Methods Enzymol. 85, 2763-2766) or the like to introduce, as appropriate, a mutation(s) to the antibody of the present invention, to prepare an antibody functionally equivalent to this antibody.

The antibody which recognizes the epitope of the CD179b protein to be recognized by the above-described anti-CD179b antibody can be obtained by a method known to those skilled in the art. Examples of the method by which it can be obtained include a method wherein the epitope of the CD179b protein recognized by the anti-CD179b antibody is determined by a normal method (e.g., epitope mapping) and an antibody is prepared using as an immunogen a polypeptide having an amino acid sequence included in the epitope; and a method wherein the epitope of the antibody is determined by a normal method, followed by selecting an antibody having the same epitope as that of the anti-CD179b antibody. Here, the term “epitope” means a polypeptide fragment having antigenicity or immunogenicity in a mammal, preferably human, and its minimum unit has about 7 to 12 amino acids.

The affinity constant Ka (K_(on)/K_(off)) of the antibody of the present invention is preferably at least 10⁷ M⁻¹, at least 10⁸ M⁻¹, at least 5×10⁸ M⁻¹, at least 10⁹ M⁻¹, at least 5×10⁹ M⁻¹, at least 10¹⁰ M⁻¹, at least 5×10¹⁰ M⁻¹ at least 10¹¹ M⁻¹, at least 5×10¹¹ M⁻¹, at least 10¹² M⁻¹, at least 10¹³ M⁻¹.

The antibody of the present invention can be conjugated with an antitumor agent. The binding between the antibody and the antitumor agent can be carried out via a spacer having a group (e.g., succinimidyl group, formyl group, 2-pyridyldithio group, maleimidyl group, alkoxycarbonyl group or hydroxy group) reactive with an amino group, carboxyl group, hydroxy group, thiol group and/or the like.

Examples of the antitumor agent include the following antitumor agents known in literatures and the like, that is, paclitaxel, doxorubicin, daunorubicin, cyclophosphamide, methotrexate, 5-fluorouracil, thiotepa, busulfan, improsulfan, piposulfan, benzodopa, carboquone, meturedopa, uredopa, altretamine, triethylenemelamine, triethylenephosphoramide, triethiylenethiophosphoramide, trimethylolomelamine, bullatacin, bullatacinone, camptothecin, bryostatin, callystatin, cryptophycin 1, cryptophycin 8, dolastatin, duocarmycin, eleutherobin, pancratistatin, sarcodictyin, spongistatin, chlorambucil, chlornaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxyhydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard, carmustine, chlorozotocin, fotemustine, lomustine, nimustine, ranimustine, calicheamicin, dynemicin, clodronate, esperamicin, aclacinomycin, actinomycin, authramycin, azaserine, bleomycin, cactinomycin, carabicin, carminomycin, carzinophilin, chromomycin, dactinomycin, detorbicin, 6-diazo-5-oxo-L-norleucine, ADRIAMYCIN, epirubicin, esorubicin, idarubicin, marcellomycin, mitomycin C, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin, denopterin, pteropterin, trimetrexate, fludarabine, 6-mercaptopurine, thiamiprine, thioguanine, ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine and floxuridine; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone, aminoglutethimide, mitotane, trilostane, frolinic acid, aceglatone, aldophosphamide glycoside, aminolevulinic acid, eniluracil, amsacrine, bestrabucil, bisantrene, edatraxate, defofamine, demecolcine, diaziquone, elfornithine, elliptinium acetate, epothilone, etoglucid, lentinan, lonidamine, maytansine, ansamitocine, mitoguazone, mitoxantrone, mopidanmol, nitraerine, pentostatin, phenamet, pirarubicin, losoxantrone, podophyllinic acid, 2-ethylhydrazide, procarbazine, razoxane, rhizoxin, schizophyllan, spirogermanium, tenuazonic acid, triaziquone, roridine A, anguidine, urethane, vindesine, dacarbazine, mannomustine, mitobronitol, mitolactol, pipobroman, gacytosine, doxetaxel, chlorambucil, gemcitabine, 6-thioguanine, mercaptopurine, cisplatin, oxaliplatin, carboplatin, vinblastine, etoposide, ifosfamide, mitoxantrone, vincristine, vinorelbine, novantrone, teniposide, edatrexate, daunomycin, aminopterin, xeloda, ibandronate, irinotecan, topoisomerase inhibitors, difluoromethylornithine (DMFO), retinoic acid and capecitabine, and pharmaceutically acceptable salts and derivatives thereof.

Alternatively, the antibody of the present invention can be linked to a known radioisotope described in a literature or the like, such as At²¹¹, I¹³¹, I¹²⁵, Y⁹⁰, Re¹⁸⁶, Re¹⁸⁸, Sm¹⁵³, Bi²¹², P³² or Lu. The radioisotope is preferably effective for therapy and/or diagnosis of a tumor.

The antibody of the present invention is an antibody having an immunological reactivity with CD179b, or an antibody which specifically recognizes CD179b. The antibody should be an antibody having a structure by which the rejection reaction can be mostly or completely avoided in the subject animal to which the antibody was administered. Examples of such an antibody include, for example, in cases where the subject animal is human, human antibodies, humanized antibodies, chimeric antibodies (e.g., human-mouse chimeric antibodies), single chain antibodies and bispecific antibodies. Each of these antibodies is a recombinant antibody wherein: each variable region in the heavy chain and the light chain is derived from a human antibody; each variable region in the heavy chain and the light chain is constituted by the complementarity-determining regions (CDR1, CDR2 and CDR3) of an antibody derived from a non-human animal and the framework regions derived from a human antibody; or each variable region in the heavy chain and the light chain is derived from a non-human animal; which recombinant antibody has human antibody-derived constant regions in the heavy chain and the light chain. The first two antibodies are preferred.

These recombinant antibodies can be prepared as follows. A DNA encoding a monoclonal antibody (for example, human monoclonal antibody, mouse monoclonal antibody, rat monoclonal antibody or chicken monoclonal antibody) against human CD179b is cloned from antibody-producing cells such as hybridomas, and, using this as a template, DNAs encoding the light chain variable region and the heavy chain variable region of the antibody is prepared by, for example, the RT-PCR method, followed by determining the sequence of the variable region or the sequences of CDR1, CDR2 and CDR3 in each of the light chain and the heavy chain according to the Kabat EU numbering system (Kabat et al., Sequences of Proteins of Immunological Interest, 5Th Ed. Public Health Service, National Institute of Health, Bethesda, Md. (1991)). Further, DNAs encoding the respective variable regions or DNAs encoding the respective CDRs are prepared using the genetic recombination technique (Sambrook et al., Molecular Cloning, Second Edition, Current Protocols in Molecular Biology (1989)) or a DNA synthesizer. Here, the above-described human monoclonal antibody-producing hybridoma can be prepared by immunizing a human antibody-producing animal (e.g., mouse) with human CD179b, followed by fusing spleen cells excised from the immunized animal with myeloma cells. In addition, as required, DNAs encoding the variable region and the constant region in the light chain or the heavy chain derived from a human antibody are prepared using the genetic recombination technique or a DNA synthesizer.

In the case of a humanized antibody, a DNA encoding the humanized antibody can be prepared by a process wherein the CDR sequences in a DNA encoding the variable region of the light chain or the heavy chain derived from a human antibody are substituted with the corresponding CDR sequences of an antibody derived from a non-human animal (e.g., mouse, rat or chicken) to prepare a DNA, and the thus obtained DNA is linked to a DNA encoding the constant region in the light chain or the heavy chain, respectively, derived from a human antibody.

In the case of a chimeric antibody, a DNA encoding the chimeric antibody can be prepared by a process wherein a DNA encoding the variable region in the light chain or the heavy chain derived from a non-human animal (e.g., mouse, rat or chicken) is linked to a DNA encoding the constant region of the light chain or the heavy chain, respectively, derived from a human antibody

In the case of a single-chain antibody, which is an antibody having a heavy chain variable region and a light chain variable region linearly linked to each other via a linker, a DNA encoding the single-chain antibody can be prepared by a process wherein a DNA encoding the heavy chain variable region, a DNA encoding the linker and a DNA encoding the light chain variable region are linked together. Here, each of the heavy chain variable region and the light chain variable region is either derived from a human antibody or derived from a human antibody in which only the CDRs were replaced by the CDRs of an antibody derived from a non-human animal (e.g., mouse, rat or chicken). Further, the linker has 12 to 19 amino acids, and examples thereof include (G₄S)₃ having 15 amino acids (Kim, G B. et al., Protein Engineering Design and Selection 2007, 20(9):425-432).

In the case of a bispecific antibody (diabody), which is an antibody capable of binding specifically to two different epitopes, a DNA encoding the bispecific antibody can be prepared, for example, by a process wherein a DNA encoding a heavy chain variable region A, a DNA encoding a light chain variable region B, a DNA encoding a heavy chain variable region B and a DNA encoding a light chain variable region A are linked together in this order (however, the DNA encoding a light chain variable region B and the DNA encoding a heavy chain variable region B are linked to each other via a DNA encoding a linker as described above). Here, each of the heavy chain variable region and the light chain variable region is either derived from a human antibody or derived from a human antibody in which only the CDRs were replaced by the CDRs of an antibody derived from a non-human animal (e.g., mouse, rat or chicken).

A recombinant antibody can be prepared by incorporating the thus prepared recombinant DNA(s) into one or more appropriate vector(s) and introducing the resulting vector(s) into host cells (e.g., mammalian cells, yeast cells and insect cells), followed by allowing (co-)expression of the recombinant DNA(s) (P. J. Delves, ANTIBODY PRODUCTION ESSENTIAL TECHNIQUES, 1997 WILEY; P. Shepherd and C. Dean, Monoclonal Antibodies, 2000 OXFORD UNIVERSITY PRESS; J. W. Goding, Monoclonal Antibodies: principles and practice, 1993 ACADEMIC PRESS).

The antibody of the present invention prepared by the above method is an antibody comprising, for example, a heavy chain variable region having the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 and a light chain variable region having the amino acid sequences shown in SEQ ID NOs:106, 107 and 108. Here, the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 are those for CDR1, CDR2 and CDR3, respectively, of a mouse antibody heavy chain variable region, and the amino acid sequences shown in SEQ ID NOs:106, 107 and 108 are those for CDR1, CDR2 and CDR3, respectively, of a mouse antibody light chain variable region. Therefore, the humanized antibody, chimeric antibody, single-chain antibody or bispecific antibody of the present invention is the following antibody, for example.

(i) An antibody comprising: a heavy chain variable region having the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 and the amino acid sequences of the framework regions derived from a human antibody; and a light chain variable region having the amino acid sequences shown in SEQ ID NOs:106, 107 and 108 and the amino acid sequences of the framework regions derived from a human antibody.

(ii) An antibody comprising: a heavy chain variable region having the amino acid sequences shown in SEQ ID NOs:103, 104 and 102 and the amino acid sequences of the framework regions derived from a human antibody; a heavy chain constant region having an amino acid sequence derived from a human antibody; a light chain variable region having the amino acid sequences shown in SEQ ID NOs:106, 107 and 108 and the amino acid sequences of the framework regions derived from a human antibody; and a light chain constant region having an amino acid sequence derived from a human antibody.

(iii) An antibody comprising: a heavy chain variable region having the amino acid sequence shown in SEQ ID NO:105; and a light chain variable region having the amino acid sequence shown in SEQ ID NO:109.

(iv) An antibody comprising: a heavy chain variable region having the amino acid sequence shown in SEQ ID NO:105; a heavy chain constant region having an amino acid sequence derived from a human antibody; a light chain variable region having the amino acid sequence shown in SEQ ID NO:109; and a light chain constant region having an amino acid sequence derived from a human antibody.

Sequences of the constant regions and the variable regions of human antibody heavy chains and light chains can be obtained from, for example, NCBI (USA: GenBank, UniGene and the like). Examples of the sequences which may be referred to include the accession number J00228 for the human IgG1 heavy chain constant region, the accession number J00230 for the human IgG2 heavy chain constant region, the accession number X03604 for the human IgG3 heavy chain constant region, the accession number K01316 for the human IgG4 heavy chain constant region, the accession numbers V00557, X64135, X64133 and the like for the human light chain κ constant region, and the accession numbers X64132, X64134 and the like for the human light chain λ constant region.

The above antibody preferably has cytotoxic activity and therefore can exert an anti-tumor effect.

Further, the specific sequences of the variable regions of the heavy chain and the light chain and the CDRs in the above antibodies are presented for the illustration purpose only, and it is apparent that they are not restricted to the specific sequences. A hybridoma which can produce another human antibody or non-human animal antibody (e.g., mouse antibody) against human CD179b is prepared, and the monoclonal antibody produced by the hybridoma is recovered, followed by judging whether or not it is an antibody of interest using as indices its immunological affinity and cytotoxicity to human CD179b. By this, a monoclonal antibody-producing hybridoma of interest is identified, and DNAs encoding the variable regions of the heavy chain and the light chain of the antibody of interest are prepared from the hybridoma as described above, followed by determining the sequences of the DNAs and then using the DNAs for preparation of the another antibody.

Further, the above antibody of the present invention may have substitution, deletion and/or addition of 1 or several (preferably, 1 or 2) amino acid(s) especially in a framework region sequence(s) and/or constant region sequence(s) in each of the antibodies (i) to (iv) above, as long as the antibody has a specificity allowing specific recognition of CD179b. Here, the term “several” means 2 to 5, preferably 2 or 3.

The present invention further provides a DNA encoding the above antibody of the present invention, a DNA encoding the heavy chain or the light chain of the above antibody or a DNA encoding the variable region of the heavy chain or the light chain of the above antibody. Examples of such a DNA include: DNAs encoding heavy chain variable regions having the base sequences encoding the amino acid sequences shown in SEQ ID NOs:103, 104 and 102; DNAs encoding light chain variable regions having the base sequences encoding the amino acid sequences shown in SEQ ID NOs:106, 107 and 108; and the like.

Since the complementarity-determining regions (CDRs) encoded by DNAs having these sequences are regions which determine the specificity of the antibody, the sequences encoding the other regions in the antibody (that is, the constant regions and the framework regions) may be those derived from another antibody. Here, although the another antibody includes antibodies derived from non-human organisms, it is preferably derived from human in view of reduction of side effects. That is, in the above-described DNA, the regions encoding the respective framework regions and the constant regions of the heavy chain and the light chain preferably have base sequences encoding corresponding amino acid sequences derived from a human antibody.

Other examples of the DNA encoding the antibody of the present invention include DNAs encoding the heavy chain variable region having a base sequence encoding the amino acid sequence shown in SEQ ID NO:105 and DNAs wherein the region encoding the light chain variable region has a base sequence encoding the amino acid sequence shown in SEQ ID NO:109. Here, examples of the base sequence encoding the amino acid sequence shown in SEQ ID NO:105 include the base sequence shown in SEQ ID NO:110. Further, examples of the base sequence encoding the amino acid sequence shown in SEQ ID NO:109 include the base sequence shown in SEQ ID NO:111. Among these DNAs, preferred are those comprising the region encoding the constant region of each of the heavy chain and the light chain, having a base sequence encoding a corresponding amino acid sequence derived from a human antibody.

The DNA of the present invention can be obtained by, for example, the above method or the following method. First, from a hybridoma related to the antibody of the present invention, total RNA is prepared using a commercially available RNA extraction kit, and cDNA is synthesized by a reverse transcriptase using random primers or the like. Subsequently, by the PCR method using as primers oligonucleotides having sequences conserved in the variable region of each of a known mouse antibody heavy chain gene and light chain gene, cDNAs encoding the antibody are amplified. The sequence encoding each constant region can be obtained by amplifying a known sequence by the PCR method. The base sequences of the DNAs can be determined by a conventional method by, for example, incorporating the sequences into plasmids or phages for sequence determination.

The anti-tumor effect of the anti-CD179b antibody used in the present invention against CD179b-expressing cancer cells is considered to be caused by the following mechanism.

The antibody-dependent cell-mediated cytotoxicity (ADCC) by effector cells against CD179b-expressing cells; and

the complement-dependent cytotoxicity (CDC) against CD179b-expressing cells.

Thus, evaluation of the activity of the anti-CD179b antibody used in the present invention can be carried out, as particularly shown in Examples below, by measuring the above-described ADCC activity or CDC activity against cancer cells expressing CD179b in vitro.

Since the anti-CD179b antibody used in the present invention binds to a CD179b protein on cancer cells and exhibits an anti-tumor action due to the above activities, the antibody is considered to be effective for therapy and/or prophylaxis of cancer. That is, the present invention provides a pharmaceutical composition for therapy and/or prophylaxis of cancer comprising as an effective component an anti-CD179b antibody. In cases where the anti-CD179b antibody is used for the purpose of administration to a human body (antibody therapy), the antibody is preferably prepared as a human antibody or a humanized antibody in order to reduce its immunogenicity.

A higher binding affinity of the anti-CD179b antibody to the CD179b protein on the cancer cell surface causes a stronger anti-tumor activity by the anti-CD179b antibody. Thus, if an anti-CD179b antibody having a higher binding affinity to the CD179b protein can be obtained, a higher anti-tumor effect can be expected, and therefore the antibody can be applied as a pharmaceutical composition for the purpose of therapy and/or prophylaxis of cancer. In terms of the higher binding affinity, the affinity constant Ka (K_(on)/K_(off)) is preferably at least 10⁷ M⁻¹, at least 10⁸ M⁻¹, at least 5×10⁸ M⁻¹, at least 10⁹ M⁻¹, at least 5×10⁹ M⁻¹, at least 10¹⁰ M⁻¹, at least 5×10¹⁰ M⁻¹, at least 10¹¹ M⁻¹, at least 5×10¹¹ M⁻¹, at least 10¹² M⁻¹, at least 10¹³ M⁻¹, as previously mentioned.

<Pharmaceutical Composition>

The target of the pharmaceutical composition of the present invention for therapy and/or prophylaxis of cancer is not restricted as long as it is a cancer (cell) expressing the CD179b gene, and preferably a cancer (cell) selected from the group consisting of leukemia, lymphoma and breast cancer, including also mammary gland cancer, combined mammary gland cancer, mammary gland malignant mixed tumor, intraductal papillary adenocarcinoma, mastocytoma, chronic lymphocytic leukemia, gastrointestinal lymphoma, digestive organ lymphoma and small/medium cell lymphoma.

Further, the antibody or a fragment thereof used in the present invention can be used for therapy and/or prophylaxis of the above-described cancers.

When the antibody used in the present invention is used as a pharmaceutical composition, it can be formulated by a method known to those skilled in the art. For example, it can be parenterally used in the form of an injection solution containing a sterile solution or suspension prepared with another pharmaceutically acceptable liquid. For example, the composition may be used in combination with a pharmaceutically acceptable carrier(s) and/or medium/media, such as sterile water, physiological saline, vegetable oil, emulsifier, suspending agent, surfactant, stabilizer, flavoring agent, excipient, vehicle, antiseptic and/or binder, which is/are mixed into the form of a unit dose required for carrying out formulation which is generally accepted. The amount of the effective component in the formulation is determined such that an appropriate volume is obtained within the prescribed range.

The sterile composition for injection can be prescribed using a vehicle such as distilled water for injection, according to a conventional formulation method.

Examples of the aqueous solution include isotonic solutions containing physiological saline, glucose and/or an adjunct(s) such as D-sorbitol, D-mannose, D-mannitol and/or sodium chloride, which may be used in combination with an appropriate solubilizer(s) such as an alcohol, in particular, ethanol; polyalcohol such as propylene glycol; polyethylene glycol; nonionic surfactant such as polysorbate 80 (TM); and/or HCO-60.

Examples of the oily liquid include sesame oils and soybean oils, which may be used in combination with benzyl benzoate or benzyl alcohol as a solubilizer. Further, a buffering agent such as phosphate buffer or sodium acetate buffer; soothing agent such as procaine hydrochloride; and/or stabilizer such as benzyl alcohol, phenol or antioxidant may also be blended. The prepared injection solution is usually filled into an appropriate ampoule.

The administration is carried out orally or parenterally, preferably parenterally, and particular examples thereof include the injection solution type, nasal administration type, pulmonary administration type and percutaneous administration type. Examples of the injection solution type include intravenous injection, intramuscular injection, intraperitoneal administration and subcutaneous injection, by which the injection solution can be administered systemically or topically.

Further, the method of administration can be appropriately selected depending on the age, symptom, sex and the like of the patient. The dose of the pharmaceutical composition containing the antibody or a fragment thereof can be selected within the range of, for example, 0.0001 mg to 1000 mg per 1 kg of the body weight per one time. Alternatively, the dose can be selected within the range of 0.001 to 100000 mg/body per patient, but the dose is not restricted to these values. The dose and the method of administration vary depending on the body weight, age, symptom and the like of the patient, and those skilled in the art can appropriately select them.

<Polypeptide and DNA>

The present invention further provides the following polypeptides and DNAs related to the above antibody.

(i) A polypeptide having the amino acid sequence shown in SEQ ID NO:105, and a DNA encoding the polypeptide.

(ii) A polypeptide having the amino acid sequence shown in SEQ ID NO:109, and a DNA encoding the polypeptide.

(iii) A DNA having the base sequence shown in SEQ ID NO:110.

(iv) A DNA having the base sequence shown in SEQ ID NO:111.

(v) A heavy chain CDR polypeptide selected from the group consisting of the amino acid sequences shown in SEQ ID NOs:103, 104 and 102, and a DNA encoding the polypeptide.

(vi) A light chain CDR polypeptide selected from the group consisting of the amino acid sequences shown in SEQ ID NOs:106, 107 and 108, and a DNA encoding the polypeptide.

These polypeptides and DNAs may be prepared using the genetic recombination technique as described above.

EXAMPLES

The present invention will now be described concretely by way of Examples, but the scope of the present invention is not restricted by these particular examples.

Example 1 Identification of a Novel Cancer Antigen by the SEREX Method

(1) Preparation of a cDNA Library

From a canine mammary gland cancer tissue removed by surgery, total RNA was extracted by the Acid guanidium-Phenol-Chloroform method, and poly(A)⁺ RNA was purified using the Oligotex-dT30 mRNA purification Kit (manufactured by Takara Shuzo Co., Ltd.) according to the protocol described in the attached instructions.

Using the thus obtained mRNA (5 μg), a canine mammary gland cancer-derived cDNA phage library was synthesized. For preparation of the cDNA phage library, cDNA Synthesis Kit, ZAP-cDNA Synthesis Kit and ZAP-cDNA GigapackIII Gold Cloning Kit (manufactured by STRATAGENE) were used according to the protocols described in the attached instructions. The size of the prepared cDNA phage library was 2.99×10⁵ pfu/ml.

(2) Screening of the cDNA Library by Serum

Using the canine mammary gland cancer-derived cDNA phage library prepared as described above, immunoscreening was carried out. More particularly, host E. coli (XL1-Blue MRF′) was infected with the library such that 2340 clones were included in a (I) 90×15 mm NZY agarose plate, followed by culture at 42° C. for 3 to 4 hours to allow formation of plaques. The plate was covered with a nitrocellulose membrane (Hybond™ C Extra; manufactured by GE Healthcare Bio-Science) impregnated with IPTG (isopropyl impregnated with IPTG (isopropyl-(β-D-thiogalactoside) at 37° C. for 4 hours, to allow induction and expression of proteins, thereby transferring the proteins to the membrane. Thereafter, the membrane was recovered and soaked in TBS (10 mM Tris-HCl, 150 mM NaCl pH 7.5) supplemented with 0.5% non-fat dry milk, followed by being shaken at 4° C. overnight to suppress nonspecific reactions. This filter was allowed to react with 500-fold diluted patient dog serum at room temperature for 2 to 3 hours.

As the above-described patient dog serum, a total of 3 serum samples were used which were collected from each of the dog from which the above mammary gland cancer was removed and another mammary gland cancer patient dog. These sera were stored at −80° C. and pretreated immediately before use. The pretreatment of the sera was carried out by the following method. That is, host E. coli (XL1-BLue MRF′) was infected with λ ZAP Express phage into which no exogenous gene was inserted, and cultured on a NZY plate at 37° C. overnight. Subsequently, 0.2 M NaHCO₃ buffer (pH 8.3) containing 0.5 M NaCl was added to the plate, and the plate was left to stand at 4° C. for 15 hours, followed by recovering the supernatant as an E. coli/phage extract. Thereafter, the recovered E. coli/phage extract was passed through a NHS-column (manufactured by GE Healthcare Bio-Science) to immobilize the proteins derived from the E. coli/phage. The serum from the patient dog was passed through this protein-immobilized column and allowed to react with the proteins, thereby removing antibodies that adsorb to E. coli and the phage from the serum. The serum fraction passed through the column without being adsorbed was 500-fold diluted with TBS supplemented with 0.5% non-fat dry milk, and the resulting dilution was used as a material for the immunoscreening.

The membrane to which the thus treated serum and the above-described fusion proteins were blotted was washed with TBS-T (0.05% Tween 20/TBS) 4 times, and a goat anti-dog IgG (Goat anti Dog IgG-h+I HRP conjugated; manufactured by BETHYL Laboratories, Inc.) which was 5000-fold diluted with TBS supplemented with 0.5% non-fat dry milk was allowed, as a secondary antibody, to react at room temperature for 1 hour. Detection was carried out by an enzymatic coloring reaction using the NBT/BCIP reaction solution (manufactured by Roche), and colonies whose positions were identical to those of positive sites of the coloring reaction were collected from the Φ90×15 mm NZY agarose plate, and dissolved into 500 μl of SM buffer (100 mM NaCl, 10 mM MgClSO₄, 50 mM Tris-HCl, 0.01% gelatin, pH7.5). The second and third screenings were carried out by repeating the same method as described above until the colonies positive in the coloring reaction became single colonies, thereby isolating 45 positive clones after screening of 92820 phage clones reactive with IgG in the serum.

Homology Search of the Isolated Antigen Genes

To subject the 45 positive clones isolated by the above method to sequence analysis, an operation to convert the phage vector to a plasmid vector was carried out. More particularly, 200 μl of a solution prepared such that the host E. coli (XL1-Blue MRF′) was contained to an absorbance OD₆₀₀ of 1.0, 250 μl of the purified phage solution and 1 μl of ExAssist helper phage (manufactured by STRATAGENE) were mixed together, and the resulting mixture was allowed to react at 37° C. for 15 minutes, followed by adding 3 ml of LB broth thereto and culturing the resultant at 37° C. for 2.5 to 3 hours. This was immediately followed by 20 minutes of incubation in a water bath at 70° C. and centrifugation at 1000×g for 15 minutes, after which the supernatant was collected as a phagemid solution. Subsequently, 200 μl of a solution prepared such that the phagemid host E. coli (SOLR) was contained to an absorbance OD₆₀₀ of 1.0 and 10 μl of the purified phagemid solution were mixed together, and the resulting mixture was allowed to react at 37° C. for 15 minutes, followed by plating a 50 μl aliquot of the resultant on LB agar medium supplemented with ampicillin (50 μg/ml final concentration) and culturing at 37° C. overnight. Single colonies of the transformed SOLR were picked up and cultured in LB medium supplemented with ampicillin (50 μg/ml final concentration) at 37° C., followed by purifying plasmid DNAs having inserts of interest using QIAGEN plasmid Miniprep Kit (manufactured by QIAGEN).

Each purified plasmid was subjected to analysis of the full-length sequence of the insert by the primer walking method using the T3 primer shown in SEQ ID NO:94 and the T7 primer shown in SEQ ID NO:95. By this sequence analysis, the gene sequences shown in the even number IDs of SEQ ID NOs:4 to 92 were obtained. Using the base sequences and the amino acid sequences (odd number IDs of SEQ ID NOs: 5 to 93) of these genes, homology search against known genes were carried out using a homology search program BLAST (http://www.ncbi.nlm.nih.gov/BLAST/), and, as a result, it was revealed that all the obtained 45 genes were those encoding CD179b. The homologies among the 45 genes were 94 to 99% in terms of the base sequences and 96 to 99% in terms of the amino acid sequences. The homologies between these genes and the gene encoding a human homologous factor were 62 to 82% in terms of the base sequences and 69 to 80% in terms of the amino acid sequences, in the region translated to a protein. The base sequence of the human homologous factor is shown in SEQ ID NO:1, and the amino acid sequences of the human homologous factor are shown in SEQ ID NOs:2 and 3.

(4) Analysis of Gene Expression in Each Tissue

Expressions of the genes obtained by the above method in dog and human normal tissues and various cell lines were investigated by the RT-PCR (Reverse Transcription-PCR) method. The reverse transcription reaction was carried out as follows. That is, from 50 to 100 mg of each tissue or 5-10×10⁶ cells of each cell line, total RNA was extracted using the TRIZOL reagent (manufactured by INVITROGEN) according to the protocol described in the attached instructions. Using this total RNA, cDNA was synthesized by the Superscript First-Strand Synthesis System for RT-PCR (manufactured by INVITROGEN) according to the protocol described in the attached instructions. As the cDNAs of human normal tissues (brain, hippocampus, testis, colon and placenta), Gene Pool cDNA (manufactured by INVITROGEN), QUICK-Clone cDNA (manufactured by CLONETECH) and Large-Insert cDNA Library (manufactured by CLONETECH) were used. The PCR reaction was carried out as follows, using primers specific to the obtained dog genes (shown in SEQ ID NOs:96 and 97) and their human homologous gene (shown in SEQ ID NOs:98 and 99). That is, reagents and an attached buffer were mixed such that concentrations/amounts of 0.25 μl of a sample prepared by the reverse transcription reaction, 2 μM each of the above primers, 0.2 mM each of dNTPs, and 0.65 U ExTaq polymerase (manufactured by Takara Shuzo Co., Ltd.) were attained in a total volume of 25 μl, and the reaction was carried out by repeating 30 cycles of 94° C. for 30 seconds, 60° C. for 30 seconds and 72° C. for 30 seconds using a Thermal Cycler (manufactured by Bio-Rad Laboratories, Inc.). The above-described primers specific to genes having the base sequences shown in SEQ ID NOs: 96 and 97 were for amplification of the positions 32 to 341 in the base sequence shown in SEQ ID NO:4, and for amplification of the region common to all the dog CD179b genes shown in the even number IDs of SEQ ID NOs: 4 to 92. Further, the primers specific to genes having the base sequences shown in SEQ ID NOs:98 and 99 were for amplification of the positions 216 to 738 in the base sequence shown in SEQ ID NO:1. As a control for comparison, primers specific to GAPDH (shown in SEQ ID NOs:100 and 101) were used at the same time. As a result, as shown in FIG. 1, the obtained dog genes did not show expression in normal dog tissues at all, but showed strong expression in canine breast cancer tissues. In terms of expression of the human homologous gene, bone marrow was the only human normal tissue wherein its expression was confirmed, but, in human cancer cells, its expression was detected in leukemia cell lines and breast cancer cell lines, so that specific expression of CD179b in the leukemia cell lines and the breast cancer cell lines was confirmed.

In FIG. 1, reference numeral 1 in the ordinate represents the expression pattern of the gene identified as above, and reference numeral 2 represents the expression pattern of the GAPDH gene as the control for comparison.

(5) Analysis of Expression of the Antigen Protein on Cancer Cells

Subsequently, each cancer cell line wherein expression of the CD179b gene was confirmed was investigated for whether or not the CD179b protein is expressed on the cell surface. In a 1.5 ml microcentrifuge tube, 10⁶ cells of each human cancer cell line for which expression of the gene was observed were placed, which tube was then centrifuged. To this tube, 5 μl of mouse anti-human CD179b antibody (clone name: GA170; manufactured by Santa Cruz Biotechnology) was added, and the resultant was suspended in 95 μl of PBS supplemented with 0.1% fetal calf serum, followed by leaving the resulting suspension to stand on ice for 1 hour. After washing the cells with PBS, the cells were suspended in 5 μl of FITC-labeled rabbit anti-mouse IgG2a monoclonal antibody (manufactured by BD Pharmingen) and 95 μl of PBS supplemented with 0.1% fetal bovine serum, and left to stand on ice for 1 hour. After washing the cells with PBS, fluorescence intensity was measured by FACSCalibur manufactured by Beckton Dickinson. On the other hand, the same operation as described above was carried out to prepare the cells as a control, using mouse IgG2a Isotype control (manufactured by MBL) instead of the mouse anti-human CD179b antibody. As a result, the cells to which the anti-human CD179b antibody was added showed a fluorescence intensity not less than 10% higher than that of the control, and therefore it was confirmed that the CD179b protein is expressed on the cell membrane surface of the above human cancer cell line.

Example 2 Anti-tumor Effect, Against Cancer Cells, of the Antibody Against CD179b

(1) The ADCC Activity

Thereafter, whether or not the antibody against CD179b can damage tumor cells expressing CD179b was studied. The evaluation was carried out using a commercially available mouse antibody against human CD179b (clone name: GA170). Into a 50 ml centrifuge tube, 10⁶ cells belonging to each of the 3 types of human leukemia cells, Namalwa, BDCM and RPMI1788 (all of these were purchased from ATCC), whose expression of CD179b was confirmed in Example 1(5), were collected, and 100 μCi of chromium 51 was added to the tube, followed by incubation at 37° C. for 2 hours. Thereafter, the cells were washed 3 times with RPMI medium supplemented with 10% fetal calf serum, and placed in a 96-well V-bottom plate in an amount of 10³ cells/well. To each well, 1 μg of GA170 was added, and 2×10⁵ lymphocytes separated from mouse spleen were further added thereto, followed by culture under the conditions of 37° C., 5% CO₂ for 4 hours. Thereafter, the amount of chromium 51 in the culture supernatant released from damaged tumor cells was measured, and the ADCC activity by GA170 against each type of cancer cells was calculated. As a result, ADCC activities of 32.6%, 32.3% and 28.3% were confirmed for Namalwa, BDCM and RPMI1788, respectively. On the other hand, when an isotype control (clone name: 6H3) of GA170 was used for the same operation, the above activity was not detected. Thus, it was revealed that, by the ADCC activity induced using an antibody against CD179b, tumor cells expressing CD179b can be damaged.

The cytotoxic activity was obtained as a result of a process wherein the antibody against CD179b used in the present invention, mouse lymphocytes, and 10³ cells of each leukemia cell line were mixed together, followed by culturing the cells for 4 hours, measuring the amount of chromium 51 released into the medium after the culture, and calculating the cytotoxic activity against the leukemia cell line according to the following calculation equation*. *Equation: Cytotoxic activity (%)=the amount of chromium 51 released from Namalwa, BDCM or RPMI1788 upon addition of the antibody against CD179b and mouse lymphocytes/the amount of chromium 51 released from the target cells upon addition of 1N hydrochloric acid×100. (2) The CDC Activity

Blood collected from a rabbit was placed in an Eppendorf tube, and left to stand at room temperature for 60 minutes, followed by centrifugation at 3000 rpm for 5 minutes to prepare serum for measurement of the CDC activity. Into a 50 ml centrifuge tube, 10⁶ cells belonging to each of the 3 types of human leukemia cells, Namalwa, BDCM and RPMI1788 were collected, and 100 μCi of chromium 51 was added to the tube, followed by incubation at 37° C. for 2 hours and washing the cells 3 times with RPMI medium supplemented with 10% fetal calf serum. Thereafter, the cells were suspended in RPMI medium containing the rabbit serum prepared as above in an amount of 50%, and placed in a 96-well V-bottom plate in an amount of 10³ cells/well. To each well, 1 μg of GA170 was added, followed by culture under the conditions of 37° C., 5% CO₂ for 4 hours. Thereafter, the amount of chromium 51 in the culture supernatant released from damaged tumor cells was measured, and the CDC activity by GA170 against each cancer cells was calculated. As a result, CDC activities of 30.5%, 21.2% and 30.5% were confirmed for Namalwa, BDCM and RPMI1788, respectively. On the other hand, when an isotype control (clone name: 6H3) of GA170 was used for the same operation, the above activity was not detected. Thus, it was revealed that, by the CDC activity induced using an antibody against CD179b, tumor cells expressing CD179b can be damaged.

The cytotoxic activity was obtained, as in the above (1), as a result of calculation of the cytotoxic activity against each leukemia cell line according to the following calculation equation*. *Equation: Cytotoxic activity (%)=the amount of chromium 51 released from Namalwa, BDCM or RPMI1788 upon addition of the antibody against CD179b, and rabbit serum/the amount of chromium 51 released from the target cells upon addition of 1N hydrochloric acid×100.

Example 3 Preparation of a Monoclonal Antibody

(1) Preparation of an Antigen Protein

The human CD179b protein was prepared by the method of lipofection to animal cells. The human CD179b gene (SEQ ID NO:22) was introduced to a vector encoding the human IgG1Fc region, the SRaIgG1Fc vector, via restriction sites XhoI and BamHI. The SRaIgG1Fc vector is a vector prepared by introduction of the gene for the human IgG1 Fc region into the pcDL-SRa296 vector (manufactured by DNAX). Subsequently, 24 pg of the plasmid was mixed with 60 μl of Lipofectamine 2000 (manufactured by Invitrogen), and OPTI-MEM (manufactured by Invitrogen) was added to the resulting mixture to attain a total volume of 3 ml, followed by leaving the mixture to stand at room temperature for not less than 20 minutes. To CHO-K1 cells preliminarily prepared to 2×106 cells/12 ml OPTI MEM, 3 ml of the abovementioned mixed solution of the plasmid was added, followed by 8 hours of culture under the conditions of 37° C. and 5% CO₂. The medium was replaced with 10 ml of CHO-SSFM medium (manufactured by Invitrogen), and culture was then carried out for 4 to 5 days. Purification of the antigen protein produced in the obtained culture supernatant was carried out using ProteinA Sepharose® HP (manufactured by GE Healthcare). ProteinA Sepharose® HP was sufficiently equilibrated with 20 mM phosphate buffer (pH 7.4)/0.15 M NaCl (equilibration buffer/washing buffer), and a solution prepared by mixing the culture supernatant with the equilibration buffer at a ratio of 1:1 was introduced thereto. Subsequently, the column was washed sufficiently with the washing buffer, and elution was carried out with 0.2 M Glycine buffer (pH 2.5). The eluted solution was neutralized by addition of 1 M Tris (pH 9), and the buffer was exchanged by ultrafiltration using 20 mM phosphate buffer (pH 7.4)/0.15 M NaCl, to prepare the human CD179b protein.

(2) Obtaining Hybridomas

With an equal amount of the MPL+TDM adjuvant (manufactured by Sigma), 100 μg of the antigen protein (human CD179b protein) prepared in (1) was mixed, to prepare an antigen solution for each individual of mouse. The antigen solution was intraperitoneally administered to a Balb/c mouse (Japan SLC, Inc.) of 6 weeks old, and 3 more times of administrations were then carried out at intervals of 1 week, thereby completing immunization. Spleen removed 3 days after the last immunization was placed between 2 sterile slide glasses and ground, followed by repeating 3 times of operations wherein the cells were washed with PBS(−) (manufactured by Nissui Pharmaceutical Co., Ltd.) and centrifuged at 1500 rpm for 10 minutes to remove the supernatant, thereby obtaining spleen cells. The obtained spleen cells and mouse myeloma cells SP2/0 (purchased from ATCC) were mixed together at a ratio of 10:1, and a PEG solution warmed to 37° C. prepared by mixing 200 μl of RPMI1640 medium supplemented with 10% fetal calf serum and 800 μl of PEG1500 (manufactured by Boehringer) together was added to the resulting mixture, followed by leaving the mixture to stand for 5 minutes, thereby carrying out cell fusion. The supernatant was removed by 5 minutes of centrifugation at 1700 rpm, and the cells were suspended in 150 ml of RPMI1640 medium (HAT selection medium) supplemented with 15% fetal calf serum, to which 2% equivalent of HAT solution manufactured by Gibco was added. On each well of 15 96-well plates (manufactured by Nunc), 100 μl of the cell suspension was seeded. The cells were cultured for 7 days under the environment of 37° C., 5% CO₂, to obtain hybridomas produced by fusion of the spleen cells and the myeloma cells.

(3) Selection of the Hybridomas

Using as indices the binding affinities, against the human CD179b protein, of the antibodies produced by the prepared hybridomas, hybridomas were selected. In each well of a 96-well plate, 100 μl of 1 μg/ml solution of the human CD179b protein prepared in the above (1) was placed, and the solution was left to stand at 4° C. for 18 hours. Each well was washed with PBS-T 3 times, and 400 μl of 0.5% BSA (Bovine Serum Albumin) solution (manufactured by Sigma) was added to each well, followed by leaving the plate to stand at room temperature for 3 hours. The solution was removed, and the wells were washed 3 times with 400 μl/well of PBS-T, followed by adding 100 μl/well of the culture supernatant of each of the hybridomas obtained in the above (2) and leaving the plate at room temperature for 2 hours. After washing the wells 3 times with PBS-T, 100 μl of an HRP-labeled anti-mouse IgG (H+L) antibody (manufactured by Invitrogen) 5000-fold diluted with PBS was added to each well, and the plate was left to stand at room temperature for 1 hour. The wells were washed 3 times with PBS-T, and 100 μl of TMB substrate solution (manufactured by Thermo) was added to each well, followed by leaving the plate to stand for 15 to 30 minutes to carry out coloring reaction. After allowing coloration, 100 μl of 1 N sulfuric acid was added to each well to stop the reaction, and the absorbance at 450 nm to 595 nm was measured using an absorption spectrometer. As a result, hybridomas producing the antibodies showing the highest absorbance was selected.

The selected hybridomas were placed in a 96-well plate such that each well contains 0.5 cell, and cultured. One week later, hybridomas forming single colonies in the wells were observed. The cells in these wells were further cultured to obtain 60 cloned hybridoma cell lines.

Subsequently, a hybridoma cell line was selected using as indices the binding affinities, against leukemia cells, of the antibodies produced by the above 60 hybridoma cell lines. In each well of a 96-well plate, 100 μl of 1 mg/ml poly-L-lysine (manufactured by Sigma)-PBS solution was placed, and the plate was left to stand at room temperature for 30 minutes. After removing the poly-L-lysine-PBS solution, an operation of filling sterile distilled water in each well and discarding it was repeated 3 times, followed by air-drying of the plate in a clean bench. Namalwa, a human leukemia cell line for which expression of CD179b was confirmed was suspended in PBS(−) such that a cell density of 10⁶ cells/ml was attained, and 100 μl of the resulting suspension was added to each well of the above plate, followed by leaving the plate to stand at room temperature for 15 minutes. After centrifugation at 1700 rpm for 5 minutes, the supernatant was removed, and 100 μl of 0.05% glutaraldehyde (manufactured by Sigma)-PBS solution was added to each well, followed by leaving the plate to stand at room temperature for 10 minutes. Each well was washed with PBS-T 3 times, and 300 μl of 0.5% BSA solution was added to each well, followed by leaving the plate to stand at 4° C. for 18 hours. After washing the wells 3 times with PBS-T, 100 μl of the culture supernatant of each of the 60 hybridoma cell lines obtained as above was added to the well, and the plate was left to stand at room temperature for 2 hours. The supernatant was removed and the wells were washed 3 times with PBS-T, followed by adding 100 μl of an HRP-labeled anti-mouse IgG (H+L) antibody 5000-fold diluted with PBS to each well and leaving the plate to stand at room temperature for 1 hour. The wells were washed 3 times with PBS-T, and 100 μl of TMB substrate solution (manufactured by Thermo) was added to each well, followed by leaving the plate to stand for 30 minutes to carry out coloring reaction. After allowing coloration, 100 μl of 1 N sulfuric acid was added to each well to stop the reaction, and the absorbance at 450 nm to 595 nm was measured using an absorption spectrometer. As a result, the hybridoma cell line #8, which produces the antibody showing the highest absorbance, was selected.

The isotype of the anti-CD179b monoclonal antibody #8 produced by the hybridoma cell strain #8 selected as described above was determined by the ELISA method. The culture supernatant of the hybridoma cell strain #8 was evaluated with the sub-isotyping kit (COSMO BIO Co., Ltd.) according to the protocols described in the attached instructions, and, as a result, the anti-CD179b monoclonal antibody was revealed to be IgG3.

Example 4 The Anti-Tumor Effect of the Anti-CD179b Monoclonal Antibody #8

(1) Preparation of the Anti-CD179b Monoclonal Antibody #8

The hybridoma cell strain #8 was cultured in Hybridoma SFM (manufactured by Invitrogen). The culture fluid was centrifuged at 1500 rpm for 10 minutes, and passed through a filter system 0.22 gin. For purification of the antibody, a Hitrap ProteinA Sepharose® FF (manufactured by GE Healthcare) column was used. The column was washed with PBS for equilibration. Subsequently, the culture supernatant was introduced to the column, followed by washing the column with PBS. Elution was carried out with 0.1M Glycine-HCl (pH2.5) to obtain a purified antibody.

The Anti-tumor Effect In Vitro (on Cells)

The ADCC Activity

Whether or not the anti-CD179b monoclonal antibody #8 can damage tumor cells expressing human CD179b was studied. Human leukemia cells Namalwa, for which expression of human CD179b was confirmed, were collected into a 50 ml centrifuge tube in an amount of 10⁶ cells, and 10 μCi of chromium 51 was added to the tube, followed by incubation at 37° C. for 2 hours. Thereafter, the cells were washed 3 times with RPMI medium supplemented with 10% fetal calf serum, and placed in a 96-well V-bottom plate in an amount of 10³ cells/well. To each well, 2 μg of the anti-CD179b monoclonal antibody #8 was added, and 2×10⁵ lymphocytes separated from mouse spleen were further added thereto, followed by culture under the conditions of 37° C., 5% CO₂ for 4 hours. Thereafter, the amount of chromium 51 in the culture supernatant released from damaged tumor cells was measured, and the ADCC activity by the anti-CD179b monoclonal antibody #8 against the Namalwa cells was calculated. As a result, an ADCC activity of 60.6% was confirmed for Namalwa in each well. On the other hand, when an isotype control (clone name: ME07) was used in a similar operation, the above activity was not detected. Thus, it was revealed that the anti-CD179 monoclonal antibody #8 can damage tumor cells expressing CD179b by its ADCC activity.

The CDC Activity

Blood collected from a rabbit was placed in an Eppendorf tube, and left to stand at room temperature for 60 minutes, followed by centrifugation at 3000 rpm for 5 minutes to prepare serum for measurement of the CDC activity. Into a 50 ml centrifuge tube, 10⁶ cells of Namalwa, which are human leukemia cells, were collected, and 100 μCi of chromium 51 was added to the tube, followed by incubation at 37° C. for 2 hours and washing the cells 3 times with RPMI medium supplemented with 10% fetal calf serum. Thereafter, the cells were suspended in RPMI medium containing the rabbit serum prepared as described above in an amount of 50%, and placed in a 96-well V-bottom plate in an amount of 10³ cells/well. To each well, 2 μg of the anti-CD179b monoclonal antibody #8 was added, followed by culture under the conditions of 37° C., 5% CO₂ for 4 hours. Thereafter, the amount of chromium 51 in the culture supernatant released from damaged tumor cells was measured, and the CDC activity by the anti-CD179b monoclonal antibody #8 against the Namalwa cells was calculated. As a result, a CDC activity of 30.5% was confirmed for Namalwa. On the other hand, when an isotype control (clone name: ME07) was used in a similar operation, the above activity was not detected. Thus, it was revealed that the anti-CD179b monoclonal antibody #8 can damage tumor cells expressing CD179b by its CDC activity.

(3) The Anti-Tumor Effect in the Living Body of a Mouse

The anti-tumor activity of the anti-CD179b monoclonal antibody #8 in the living body of a tumor-bearing mouse was evaluated. The antibody used was prepared by purifying the culture supernatant of the hybridoma cell strain #8 by a column in the same manner as described above.

Using a tumor-bearing mouse to which a cancer cell line derived from human which expresses CD179b was transplanted, the anti-tumor activity of the anti-CD179b monoclonal antibody #8 was evaluated. The Namalwa cells were subcutaneously transplanted to the back of each of 20 nude mice (BALB/c Slc-nu/nu, derived from Japan SLC, Inc.) in an amount of 10⁶ cells, and the tumor was allowed to grow to a size of about 7 mm in diameter. Among these mice, each of 10 tumor-bearing mice was subjected to administration of 10⁷ lymphocytes separated from peripheral blood of BALB/c mice (BALB/c Cr Slc, derived from Japan SLC, Inc.) and 300 μg of the anti-CD179b monoclonal antibody #8 from a caudal vein. Thereafter, the same amounts of the mouse lymphocytes and the antibody were administered to each tumor-bearing mouse from a caudal vein a total of 3 times in 2 days, and the size of the tumor was measured every day, thereby evaluating the anti-tumor effect. On the other hand, to each of the remaining 10 tumor-bearing mice, PBS(−) was administered instead of the above antibody, to provide a control group. As a result of this study, in the group wherein the anti-CD179b antibody was administered, the tumor volume reduced to 65% on Day 8 with respect to the tumor volume at the beginning of the administration of the antibody, which was defined as 100%. On Day 11, Day 17 and Day 20, the tumor regressed to 52%, 45% and 35%, respectively (see FIG. 2). On the other hand, in the control group, on Day 8, Day 11, Day 17 and Day 20, the tumor grew to about 180%, 220%, 350% and 420% (see FIG. 2). From these results, it was shown that the obtained anti-CD179b monoclonal antibody #8 exerts a strong anti-tumor effect in the living body, against cancer cells expressing CD179b. In terms of the size of the tumor, the volume was calculated using the calculation equation: longer diameterxshorter diameter×shorter diameter×0.5.

Example 5 Cloning of the Gene for the Variable Region of the Anti-CD179b Monoclonal Antibody #8

From the hybridoma cell line #8, mRNA was extracted, and the genes for the heavy chain variable (VH) region and the light chain variable (VL) region of the anti-CD179b monoclonal antibody #8 were obtained by the RT-PCR method using primers specific to a mouse leader sequence and the antibody constant region of IgG3. For determination of their sequences, these genes were cloned into the pCR2.1 vector (manufactured by Invitrogen).

(1) RT-PCR

From 10⁶ cells of the hybridoma cell strain #8, mRNA was prepared using the mRNA micro purification kit (manufactured by GE Healthcare), and the obtained mRNA was reverse-transcribed to synthesize cDNA using the SuperScript II 1st strand synthesis kit (manufactured by Invitrogen). These operations were carried out according to the protocols described in the attached instructions of the respective kits.

Using the obtained cDNA, the antibody genes were amplified by the PCR method. To obtain the gene for the VH region, a primer specific to the mouse leader sequence (SEQ ID NO:112) and a primer specific to the mouse IgG3 constant region (SEQ ID NO:113) were used. Further, to obtain the gene for the VL region, a primer specific to the mouse leader sequence (SEQ ID NO:114) and a primer specific to the mouse κ chain constant region (SEQ ID NO:115) were used. These primers were designed referring to Jones ST and Bending MM Bio/technology 9, 88-89 (1991). For the PCR, Ex Taq (manufactured by TAKARA BIO INC.) was used. To 5 μl of 10×EX Taq Buffer, 4 μl of dNTP Mixture (2.5 mM), 2 μl each of the primers (1.0 μM) and 0.25 μl of Ex Taq (5 units/μl), a cDNA sample was added, and sterile water was added to the resulting mixture to a total volume of 50 μl. The reaction was carried out under the conditions of 2 minutes of treatment at 94° C. followed by 30 cycles of the combination of denaturation at 94° C. for 1 minute, annealing at 58° C. for 30 seconds and the extension reaction at 72° C. for 1 minute.

(2) Cloning

Using each of the PCR products obtained as described above, electrophoresis was carried out with agarose gel, and the DNA band corresponding to each of the VH region and the VL region was excised. Each DNA fragment was processed using the QIAquick Gel purification kit (manufactured by QIAGEN) according to the protocol described in the attached instructions. Each purified DNA was cloned into the pCR2.1 vector using the TA cloning kit (manufactured by Invitrogen). The vector to which the DNA was linked was used for transformation of DH5a competent cells (manufactured by TOYOBO) according to a conventional method. Ten clones each of the transformants were cultured in a medium (100 μg/ml ampicillin) at 37° C. overnight, and each plasmid DNA was purified using the Qiaspin Miniprep kit (manufactured by QIAGEN).

(3) Determination of the Sequences

The analysis of the gene sequences of the VH region and the VL region was carried out by analyzing the plasmid DNAs in (2) using the M13 forward primer (SEQ ID NO:116) and the M13 reverse primer (SEQ ID NO:117), by a fluorescent sequencer (DNA sequencer 3130XL manufactured by ABI), using the BigDye Terminator Ver. 3.1 Cycle Sequencing kit according to the protocol in the attached instructions. As a result, the respective gene sequences were determined (identical among the 10 clones for each gene). The amino acid sequence of the VH region of the anti-CD179b monoclonal antibody #8 is shown in SEQ ID NO:105, and the amino acid sequence of the VL region of the antibody is shown in SEQ ID NO:109.

INDUSTRIAL APPLICABILITY

The antibody of the present invention is useful for therapy and/or prophylaxis of cancer.

Sequence Listing Free Text

SEQ ID NOs:94, 96 to 99: primers

SEQ ID NO:95: T7 primer

SEQ ID NOs:100 and 101: GAPDH primers

SEQ ID NOs:116 and 117: primers 

The invention claimed is:
 1. A polypeptide having the amino acid sequence shown in SEQ ID NO:105.
 2. A polypeptide having the amino acid sequence shown in SEQ ID NO:109.
 3. A DNA molecule comprising a nucleotide sequence encoding the polypeptide according to claim
 1. 4. A DNA molecule comprising a nucleotide sequence encoding the polypeptide according to claim
 2. 5. An antibody or a fragment thereof, which comprises a heavy chain variable region comprising the complementarity-determining region of SEQ ID NOs:103, 104, or 102, and a light chain variable region comprising the complementarity-determining region of SEQ ID NOs:106, 107, or 108, said antibody having immunoreactivity to a CD179b protein having the amino acid sequence shown in SEQ ID NO:3.
 6. The antibody or the fragment thereof according to 26, wherein said antibody comprises a heavy chain variable region comprising the CDR1 of SEQ ID NO:103, the CDR2 of SEQ ID NO: 104, and the CDR3 of SEQ ID NO: 102, and a light chain variable region comprising the CDR1 of SEQ ID NO:106, the CDR2 of SEQ ID NO:107, and the CDR3 of SEQ ID NO:108.
 7. An antibody or the fragment thereof according to claim 5, wherein said antibody comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO:105 and a light chain variable region comprising the amino acid sequence of SEQ ID NO:109. 